Difference between revisions of "Salmonella"

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Salmonella spp. are gram-negative straight rods, usually flagellated, facultative anaerobes.
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<big><center>[[Enterobacteriaceae|'''BACK TO ENTEROBACTERIACEAE''']]</center></big>
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<big><center>[[Bacteria|'''BACK TO BACTERIA''']]</center></big>
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<big><center>[[Infectious agents and parasites|'''BACK TO INFECTIOUS AGENTS AND PARASITES''']]</center></big>
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===Overview===
 
===Overview===
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*''Salmonella'' may be carried sub-clinically
 
*''Salmonella'' may be carried sub-clinically
 
*Some human strains cause enteric fever (''S. Typhi'' causes typhoid), also gastroenteritis, septicaemia or bacteraemia
 
*Some human strains cause enteric fever (''S. Typhi'' causes typhoid), also gastroenteritis, septicaemia or bacteraemia
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===Characteristics===
 
===Characteristics===
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*Gram negative bacilli
 
*Gram negative bacilli
 
*Facultative intracellular pathogens
 
*Facultative intracellular pathogens
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*Non-lactose fermentors, oxidase negative
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*Non-lactose fermentor, oxidase negative
 
*Do not produce urease or indole from tryptophan
 
*Do not produce urease or indole from tryptophan
 
*Utilise citrate as a carbon source
 
*Utilise citrate as a carbon source
 
*Reduce nitrates to nitrites
 
*Reduce nitrates to nitrites
 
*Grow on MacConkey
 
*Grow on MacConkey
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*Red colonies on brilliant green agar indicating alkalinity
 
 
*Ferment glucose to produce acid and gas
 
*Ferment glucose to produce acid and gas
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*Usually produce hydrogen sulphide - red colinies with black centre on XLD agar
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*Usually produce hydrogen sulphide
 
*Most motile with flagellae (H antigen)
 
*Most motile with flagellae (H antigen)
 
*H antigen can be in phase 1 or phase 2, depending on a genetic switch allowing for one of the H antigen genes to be transcribed at any one time
 
*H antigen can be in phase 1 or phase 2, depending on a genetic switch allowing for one of the H antigen genes to be transcribed at any one time
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===Classification===
 
===Classification===
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*Categorised into serovars depending on and H (Flagellar) antigen, e.g. ''Salmonella enterica'' subspecies ''enterica'' serovar Tymphimurium; must also determine phase of H antigen (isolates must be in phase 1 to be typed)
 
*Categorised into serovars depending on and H (Flagellar) antigen, e.g. ''Salmonella enterica'' subspecies ''enterica'' serovar Tymphimurium; must also determine phase of H antigen (isolates must be in phase 1 to be typed)
 
*Most animal and human isolates in Groups B to E   
 
*Most animal and human isolates in Groups B to E   
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===Pathogenicity===
 
===Pathogenicity===
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**Stimulate immune response on reaching the lamina propria
 
**Stimulate immune response on reaching the lamina propria
 
**Acute inflammation, possibly with ulceration; prostaglandin and cytokine production by epithelial cells; enterotoxin production damaging mucosa  
 
**Acute inflammation, possibly with ulceration; prostaglandin and cytokine production by epithelial cells; enterotoxin production damaging mucosa  
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**Phagocytosis of bacteria by [[Neutrophils|neutrophils]] and macrophages
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**Phagocytosis of bacteria by neutrophils and macrophages
 
**Bacteria either destroyed by the phagocytic cells or survive and multiply in the cells to cause systemic disease
 
**Bacteria either destroyed by the phagocytic cells or survive and multiply in the cells to cause systemic disease
 
**Resistance to phagocytosis and destruction by complement allows spread within the body - bacteraemia and septicaemia
 
**Resistance to phagocytosis and destruction by complement allows spread within the body - bacteraemia and septicaemia
 
**LPS O antigens prevent damage to bacterial cell wall by complement
 
**LPS O antigens prevent damage to bacterial cell wall by complement
 
**LPS also causes endotoxaemia, and may contribute to local inflammatory response damaging intestinal cells to cause diarrhoea
 
**LPS also causes endotoxaemia, and may contribute to local inflammatory response damaging intestinal cells to cause diarrhoea
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**Endotoxic shock during septicaemic [[Salmonellosis|salmonellosis]] due to LPS  
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**Endotoxic shock during septicaemic salmonellosis due to LPS  
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**Septicaemia may cause [[Bacterial skin infections - Pathology#Systemic bacterial infections|cyanosis of extremities]]
 
 
**Intracellular carriage if bacteria no completely removed
 
**Intracellular carriage if bacteria no completely removed
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**Invasive potential of certain strains e.g. ''Salmonella'' Dublin associated with carriage of a large plasmid, encoding genes to allow intracellular survival in macrophages and also to allow iron acquisition
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**Invasive potential of certain strains e.e ''Salmonella'' Dublin associated with carriage of a large plasmid, encoding genes to allow intracellular survival in macrophages and also to allow iron acquisition
 
**''Salmonellae'' are facultative intracellular organisms, allowing them to move from the gut in macrophages and cause a bacteraemia and lesions throughout the body
 
**''Salmonellae'' are facultative intracellular organisms, allowing them to move from the gut in macrophages and cause a bacteraemia and lesions throughout the body
 
**Possession of Pathogenicity Islands associated with virulence
 
**Possession of Pathogenicity Islands associated with virulence
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**''Salmonellae'' can persist in the gut or gall bladder
 
**''Salmonellae'' can persist in the gut or gall bladder
 
**Excreted in faeces after clinical signs disappeared - active carriage
 
**Excreted in faeces after clinical signs disappeared - active carriage
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**Bacteria can survive intracellularly, avoiding the immune system and antimicrobials
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**Bacteria can survive intracellularly, avioding the immune system and antimicrobials
 
**May have latent carriage and intermittent excretion in faeces
 
**May have latent carriage and intermittent excretion in faeces
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**Stresses e.g. transportation, illness, parturition, overcrowding promote excretion in carrier animals and may cause clinical signs to be shown
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**Stresses e.g. transportaion, illness, parturition, overcrowding promote excretion in carrier animals
 
**Tortoises, terrapins, snakes and other reptiles ofter carry ''Salmonellae''
 
**Tortoises, terrapins, snakes and other reptiles ofter carry ''Salmonellae''
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**Asymptomatic carriage allows faecal spread of infection
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**Asymptomatic carriage allows faecal spread of infection  
 +
 
  
 
===Clinical infections===
 
===Clinical infections===
  
 
*Zoonotic
 
*Zoonotic
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*Outbreaks from contaminated imported meat and bone meal
 +
*Some serotypes are host-specific, some are not
 +
*''S.'' Tymphimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry
 +
*''S. enteritidis'': non species-specific; losses in young birds; causes food poisoning in humans
 +
*''S.'' Dublin: invasive serovar; infects cattle
 +
*''S.'' Cholerae-Suis: primarily infects pigs; also causes severe human disease
 +
*''S.'' Pullorum: infects poultry; egg-transmitted; causes bacillary white diarrhoea, known as pullorum disease
 +
*''S.'' Gallinarum: infectes older birds; known as howl typhoid
 +
*''S.'' Pullorum and ''S.'' Gallinarum now rare in UK due to eradication programs including the Pullorum test (whole blood slide agglutination to detect antibody to both ''S.'' Pullorum and ''S'' Gallinarum
 +
*''S.'' Abortis-ovis: infects sheep
 +
*''S.'' Abortus-equi: infects horses outside of the UK
 +
*''S.'' Typhi, ''S.'' Paratyphi: infect humans
 
*Most human infections contracted from animals, especially poulty and cattle
 
*Most human infections contracted from animals, especially poulty and cattle
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*Some serotypes are host-specific, some infect a wide range of species
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*Bovine [[Intestines - Fibrinous/ Haemorrhagic Enteritis#Salmonellosis|Salmonellosis]]:
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*Healthy adult carnivores are resistant to [[Salmonellosis|salmonellosis]]
 
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*Clinical outcome depends on number of bacteria ingested, virulence of serotype, susceptibility of host
 
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*Young and debilitated animals susceptible
 
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*''Salmonella'' serotypes:
 
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**''S.'' Typhimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry
 
−
**''S. enteritidis'': non species-specific; losses in young birds; causes food poisoning in humans
 
−
**''S.'' Dublin: invasive serovar; infects cattle
 
−
**''S.'' Cholerae-Suis: primarily infects pigs; also causes severe human disease
 
−
**''S.'' Pullorum: infects poultry; egg-transmitted; causes bacillary white diarrhoea, known as pullorum disease
 
−
**''S.'' Gallinarum: infectes older birds; known as fowl typhoid
 
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**''S.'' Abortis-ovis: infects sheep
 
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**''S.'' Abortus-equi: infects horses outside of the UK
 
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**''S.'' Typhi, ''S.'' Paratyphi: infect humans
 
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**''S.'' Montevideo produces outbreaks from contaminated imported meat and bone meal
 
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*Enteric [[Salmonellosis|salmonellosis]]:
 
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**Enterocolitis occurs in most farm animal species affecting all ages
 
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**[[:Category:Enteritis, Ulcerative|Ulcerative enteritis]]
 
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**Fever, depression, anorexia, foul-smelling diarrhoea containing blood, mucus and epithelial casts
 
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**Dehydration and weight loss
 
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**Abortion
 
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**Fatal within days in severely young animals
 
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**Milder syndrome where endemic on farms, possibly due to acquired immunity
 
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**Chronic enterocolitis can occur in surviving pigs, cattle, horses, causing intermittent fever, soft faeces and gradual weight loss
 
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*Septicaemic [[Salmonellosis|salmonellosis]]:
 
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**Most common in calves, neonatal foals, pigs under one month
 
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**Sudden onset fever, depression, recumbency
 
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**Die within 48 hours if not treated
 
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**Persistent diarrhoea, meningitis, arthritis or pneumonia may occur in surviving animals
 
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**Found in [[Infectious Arthritis#In Horses|arthritis of horses]]
 
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**Can cause haemorrhagic disease by [[Platelet Abnormalities|secondary thrombocytopenic disease]]
 
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**''S.'' Cholerae-Suis in pigs causes blue discoloration of ears and snout; co-infection with viruses causes severe clinical forms of disease
 
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*Bovine [[Salmonellosis|salmonellosis]]:
 
 
**Syndrome of fever and diarrhoea (with dysentery), often fatal, in calves and adult cattle
 
**Syndrome of fever and diarrhoea (with dysentery), often fatal, in calves and adult cattle
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**Abdominal pain in adult cattle due to necrotic bowel
 
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**Recumbency and depression, with death after 7-10 days during severe infection - mortality up to 75% in untreated adult animals
 
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**Antibiotic treatment reduces mortality to 10%
 
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**Diarrhoea lasts for up to 2 weeks, and complete recovery may take months
 
 
**May cause abortion of pregnant cattle in absence of other signs
 
**May cause abortion of pregnant cattle in absence of other signs
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**Septicaemia in neonates; accute enteritis in older calves
 
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**Calves are dull, lethargic, inappetent, pyrexic, with profuse, fowl-smelling diarrhoea
 
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**Death in calves can occur after 2-3 days
 
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**Diarrhoea in survivors may last 2 weeks
 
 
**Caused by infection with various ''Salmonella'' serotypes, e.g. ''S.'' Dublin and ''S.'' Typhimurium  
 
**Caused by infection with various ''Salmonella'' serotypes, e.g. ''S.'' Dublin and ''S.'' Typhimurium  
 
**An important zoonosis and reportable
 
**An important zoonosis and reportable
 
**Carrier animals important for spread
 
**Carrier animals important for spread
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**''Salmonella'' Dublin:
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*A cause of [[Intestines - Ulcerative Enteritis|ulcerative enteritis]] in the pig.
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***Causes enterocolitis with blood-stained, foul-smelling diarrhoea containing mucus and epithelial cells
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*Can cause haemorrhagic disease by [[General Pathology - Haemostasis#Secondary Thrombocytopenic Disease|secondary thrombocytopenic disease]].
−
***Can cause fatal septicaemia - fever, depression, drop in milk yield; calves may develope arthritis, meningitis, pneumonia
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*''Salmonella'' in [[Bones - inflammatory#Osteomyelitis|Osteomyelitis]]
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***Abortion with no other clinical signs
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* In [[Joints - inflammatory#In Horses|arthritis of horses]]
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***Chronic infections with ''S.'' Dublin in calves cause dry gangrene of extremities due to disseminated intravascular coagulation; tips of ears, tail and limbs may slough
 
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***Can cause [[Osteomyelitis|Osteomyelitis]] in young animals
 
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***Most survivors become subclinical excretors
 
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***May become latent carriers with no excretion
 
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*<div id="Spleen">[[Salmonellosis|Salmonellosis]] in poultry:
 
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**''S.'' Pullorum and ''S.'' Gallinarum now rare in UK due to eradication programs including the Pullorum test (whole blood slide agglutination to detect antibody to both ''S.'' Pullorum and ''S'' Gallinarum)
 
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**These ''Salmonellae'' can infect the ovaries of hens and be transmitted via eggs
 
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**Pullorum disease infects young chickens and turkeys (under 3 weeks); high mortality rates; anorexia, depression, white diarrhoea; white nodules throughout lungs; focal necrosis of liver and [[Spleen - Anatomy & Physiology|spleen]]</div>
 
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**Fowl typhoid causes similar lesions to pullorum disease in young birds; septicaemic condition in adult birds with sudden death (enlarged, friable, bole-stained liver and enlarged [[Spleen - Anatomy & Physiology|spleen]]). On post mortem inspection bronzing of the organs is notable.
 
−
**Paratyphoid caused by non host-specific ''Salmonella'' serotypes, e.g. ''S.'' Enteritidis and ''S.'' Typhimurium; often subclinical infections
 
  
 
===Diagnosis===
 
===Diagnosis===
−
 
−
*History of previous outbreaks; clinical signs
 
−
*Post mortem: enterocolitis; blood-stained intestinal contents; enlarged mesenteric lymph nodes
 
−
*Laboratory confirmation by detection in faeces and blood from live animals; intestinal contents and tissue samples from dead animals
 
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*Isolation from blood or tissues confirms septicaemic salmonellosis
 
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*Heavy growth on plates innoculated with faeces or intestinal contents from infected animals suggests ''Salmonella'' as cause
 
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*Light growth may suggest carrier state
 
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*Culture specimens on BG and XLD agar; also add to enrichment broth such as selinite or tetrathionate broth; incubate plates and broth under aerobic conditions at 37 degrees centigrade for 48 hours; subculture from enrichment broth at 24 and 48 hours
 
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*Suspicious colonies should be identified biochemically by reactions in TSI agar and lysine decarboxylase
 
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*Slide agglutination using antisera for O and H antigens confirm the serotype
 
−
*The antigens in both phases of the H antigen must be identified
 
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*Phage typing is used for epidemiological studies of isolates
 
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*A rising antibody titre using paired serum samples in ELISA indicates active infection
 
  
  
 
===Treatment===
 
===Treatment===
−
 
−
*Intravenous antibiotics used to treat septicaemic salmonellosis
 
−
*Effective antimicrobials include tetracyclines, chloramphenicol, trimethoprim-sulphonamides, ampicillin, amoxicillin, 3rd generation cephalosporins, fluoroquinolones, but depend on the susceptiblity of individual isolate
 
−
*Fluid and electrolyte replacent to prevent dehydration and shock
 
  
  
 
===Control===
 
===Control===
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−
*Reduce exposure of young animals from fomites, food, water, infected animals
 
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*Avoid stresses e.g. overcrowding
 
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*Purchase animals from reliable sources and isolate incoming animals
 
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*Separate animals according to age
 
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*Rodent control, good hygiene, pasture rotation
 
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*Avoid grazing animals on pasture fertilised by slurry for at least 2 months after spreading
 
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*Attenuated live ''S.'' Typhimurium and ''S.'' Dublin vaccines used in cattle
 
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*Avoid oral prophylactic antimicrobials
 
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−
 
−
==In Reptiles==
 
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It is estimated that between 36 and 77% lizards harbour Salmonella - the most recognized reptilian zoonosis. Owners must be educated regarding the public health hazard (especially for the very young, the old and the immune compromised).
 
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[[Category:Lizard_and_Snake_Glossary]]
 
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[[Category:Enterobacteriaceae]]
 
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[[Category:Zoonoses]]
 
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[[Category:To_Do_-_Bacteria]]
 

Revision as of 20:13, 16 February 2008

BACK TO ENTEROBACTERIACEAE
BACK TO BACTERIA
BACK TO INFECTIOUS AGENTS AND PARASITES


Overview

  • Important member of the enterobacteria
  • Cause disease in humans and animals worldwide
  • Reservior of infection in poulty, pigs, rodents, cattle, dogs
  • Bacteria may be present in water, soil, animal feed, raw meat
  • Cause enteritis and systemic infection (septicaemia and abortion)
  • Salmonella may be carried sub-clinically
  • Some human strains cause enteric fever (S. Typhi causes typhoid), also gastroenteritis, septicaemia or bacteraemia

Characteristics

  • Gram negative bacilli
  • Facultative intracellular pathogens
  • Non-lactose fermentor, oxidase negative
  • Do not produce urease or indole from tryptophan
  • Utilise citrate as a carbon source
  • Reduce nitrates to nitrites
  • Grow on MacConkey
  • Ferment glucose to produce acid and gas
  • Usually produce hydrogen sulphide
  • Most motile with flagellae (H antigen)
  • H antigen can be in phase 1 or phase 2, depending on a genetic switch allowing for one of the H antigen genes to be transcribed at any one time

Classification

  • Single species, Salmonella enterica
  • Over 2400 pathogenic serotypes or serovars identified
  • Grouped into 9 groups according to Somatic, O antigen (lipopolysaccharide) by the Kauffmann-White scheme - determined by slide agglutination of the bacteria with specific antisera
  • Categorised into serovars depending on and H (Flagellar) antigen, e.g. Salmonella enterica subspecies enterica serovar Tymphimurium; must also determine phase of H antigen (isolates must be in phase 1 to be typed)
  • Most animal and human isolates in Groups B to E

Pathogenicity

  • Faecal-oral transmission
  • Infection frequently transmitted from faeces of rodents and birds
  • Young, immunocompromised animals particularly susceptible
  • Comparitively large dose required for infection due to gastric acid, normal intestinal flora and local immunity
  • Enterocolitis:
    • Acute enteritis
    • Bacteria adhere to intestinal epithelial cells in the ileum and colon, probably via fimbrae, O antigen and flagellar H antigen
    • Multiply in and destroy epithelial cells
    • Cytotoxin may cause epithelial cell damage by inhibiting protein synthesis and causing calcium escape from cells
    • Enterotoxin may induce fluid secretion into intestinal lumen
    • Degeneration of microvilli
  • Systemic disease:
    • Bacteria invade and replicate in host cells and resist phagocytosis and destruction by complement
    • Bacteria internalised by intestinal epithelial cells by inducing ruffling of cell membranes and uptake into vesicles
    • The organisms replicate within the vesicles and are released from the cells
    • Stimulate immune response on reaching the lamina propria
    • Acute inflammation, possibly with ulceration; prostaglandin and cytokine production by epithelial cells; enterotoxin production damaging mucosa
    • Phagocytosis of bacteria by neutrophils and macrophages
    • Bacteria either destroyed by the phagocytic cells or survive and multiply in the cells to cause systemic disease
    • Resistance to phagocytosis and destruction by complement allows spread within the body - bacteraemia and septicaemia
    • LPS O antigens prevent damage to bacterial cell wall by complement
    • LPS also causes endotoxaemia, and may contribute to local inflammatory response damaging intestinal cells to cause diarrhoea
    • Endotoxic shock during septicaemic salmonellosis due to LPS
    • Intracellular carriage if bacteria no completely removed
    • Invasive potential of certain strains e.e Salmonella Dublin associated with carriage of a large plasmid, encoding genes to allow intracellular survival in macrophages and also to allow iron acquisition
    • Salmonellae are facultative intracellular organisms, allowing them to move from the gut in macrophages and cause a bacteraemia and lesions throughout the body
    • Possession of Pathogenicity Islands associated with virulence
  • Carriage:
    • Salmonellae can persist in the gut or gall bladder
    • Excreted in faeces after clinical signs disappeared - active carriage
    • Bacteria can survive intracellularly, avioding the immune system and antimicrobials
    • May have latent carriage and intermittent excretion in faeces
    • Stresses e.g. transportaion, illness, parturition, overcrowding promote excretion in carrier animals
    • Tortoises, terrapins, snakes and other reptiles ofter carry Salmonellae
    • Asymptomatic carriage allows faecal spread of infection


Clinical infections

  • Zoonotic
  • Outbreaks from contaminated imported meat and bone meal
  • Some serotypes are host-specific, some are not
  • S. Tymphimurium infects many species; causes severe diarrhoea; non-invasive; causes of food poisoning in humans, e.g. from infected poultry
  • S. enteritidis: non species-specific; losses in young birds; causes food poisoning in humans
  • S. Dublin: invasive serovar; infects cattle
  • S. Cholerae-Suis: primarily infects pigs; also causes severe human disease
  • S. Pullorum: infects poultry; egg-transmitted; causes bacillary white diarrhoea, known as pullorum disease
  • S. Gallinarum: infectes older birds; known as howl typhoid
  • S. Pullorum and S. Gallinarum now rare in UK due to eradication programs including the Pullorum test (whole blood slide agglutination to detect antibody to both S. Pullorum and S Gallinarum
  • S. Abortis-ovis: infects sheep
  • S. Abortus-equi: infects horses outside of the UK
  • S. Typhi, S. Paratyphi: infect humans
  • Most human infections contracted from animals, especially poulty and cattle
  • Bovine Salmonellosis:
    • Syndrome of fever and diarrhoea (with dysentery), often fatal, in calves and adult cattle
    • May cause abortion of pregnant cattle in absence of other signs
    • Caused by infection with various Salmonella serotypes, e.g. S. Dublin and S. Typhimurium
    • An important zoonosis and reportable
    • Carrier animals important for spread
  • A cause of ulcerative enteritis in the pig.
  • Can cause haemorrhagic disease by secondary thrombocytopenic disease.
  • Salmonella in Osteomyelitis
  • In arthritis of horses

Diagnosis

Treatment

Control

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